Folks often get confused about the difference between centralized (a.k.a., asymmetrical or single ended) and distributed (a.k.a., symmetrical or dual-ended) application performance solutions. Centralized ADS solutions employ a device in a data center near a server or server cluster. The device intercepts traffic passing to and from the server(s), and directs and/or modifies the intercepted traffic. Modifications to intercepted server traffic must be understood on the user’s end, so the data center device must communicate with client software that makes sense of the modifications. The user’s browser serves as the most ubiquitous standard client; therefore, at present Centralized ADS solutions are typically deployed to deliver to Web-based applications.
Some Centralized ADS vendors provide proprietary software clients that can further accelerate Web applications as well as optimize non-Web applications. These clients provide a cost-effective alternative to Distributed ADS solutions in home offices or “micro branches”.
Distributed ADS solutions rely on a device in the data center and companion devices in remote offices. These devices are placed near WAN ingress/egress points where they can see, prioritize, and modify traffic. Because Distributed ADS solutions require access to the remote office, they are limited to private or virtual private networks. In the case of telecommuting or mobile workers, Distributed ADS vendors sometimes supply the “remote device” as software installed on the user’s PC.
A critical difference between these two approaches is where and how they can be applied. Here is a view of the centralized-distributed divide.
Another important aspect of the two approaches is that the centralized approach is inherently open and interoperable, while distributed solutions are closed and vendor specific. You can buy Centralized ADS solutions from vendors A and B as long as they operate in front of different servers. The users will continue to use the same browser to access all “enhanced” applications.
However, if you buy a Distributed ADS solution from vendors D and E, they will not interoperate. Thus to experience the full benefit of solutions D and E, you must install both in all locations, which can be costly. Furthermore, some features of D may adversely affect the work of E. Operating two different distributed solutions is tricky, and at best they work as “ships in the night” ignoring each other.
The bottom line is that you can be a multi-vendor Centralized ADS shop, but you will typically be forced to adopt a single-vendor Distributed ADS solution.